2013 Volume 51 Issue 6 Pages 563-571
The aim of this study was to determine whether accumulated short bouts of exercise can achieve the same cardiovascular benefits as a single long bout of exercise in sedentary male Japanese workers and to compare the programs’ relative effects on oxidative stress. Twenty-three sedentary male workers were randomly assigned into 2 different exercise programs: a Long-bout group, which performed a single period of continuous exercise (Long-bout group: 30 min × 1) 3 d per week, and a Short-bouts group, which performed 3 short bouts of exercise (Short-bouts group: 10 min × 3) 3 d per week. Cardiovascular risk factors, including the plasma thiobarbituric acid-reactive substances (TBARS) level, were examined at baseline and after both 10 and 20 wk. In the Long-bout group, waist circumference and maximum oxygen uptake (VO2max) significantly improved after 20 wk. The Short-bouts group demonstrated significant increases in VO2max after 10 weeks and in HDL-C after 20 wk. Plasma TBARS significantly decreased after 20 weeks in the Long-bout group and tended to decrease (but not significantly) in the Short-bouts group. These results indicate that accumulated short bouts of exercise are an effective option, especially for busy workers, for incorporating exercise into one’s lifestyle.
With the aging of the workforce, the incidence of cardiovascular risk factors such as dyslipidemia and hypertension has increased in Japan1). One recommended approach to address these issues is an increase in physical activity2). However, according to the Survey on State of Employees’ Health 2007 by the Ministry of Health, Labour, and Welfare, Japan, 30.6% of Japanese employees report regular mild or moderate physical activity, including brisk walking, calisthenics, and jogging3). This represented a slight increase compared with the previous survey (28.9% in 2002). However, adherence to an exercise program in Japanese employees is less than desirable4). One reason for employees’ low adherence to exercise programs is lack of available time5).
Many studies have shown that for improvements in physical fitness and body weight, exercise programs comprising an accumulation of several short sessions per day are as effective as those comprising longer continuous sessions6,7,8,9,10,11). The Active Guide 2013, issued by the Ministry of Health, Labour, and Welfare, Japan, also emphasizes that the accumulation of physical activity throughout the week is important for health promotion2). An exercise program that includes short bouts can be performed more frequently, especially by employees with limited time available for daily exercise. In their review, Murphy et al. found that most studies reported no difference in the effect on cardiovascular fitness between accumulated and continuous patterns of exercise12). However, whether accumulated exercise is as effective as continuous exercise in terms of adiposity, the lipid profile, and glucose metabolism remains unclear.
Oxidative stress is associated with the pathogenesis and progression of such cardiovascular risk factors as adiposity, high blood pressure, dyslipidemia, and glucose intolerance and is detectable before the onset of clinically significant disease13,14,15,16). Continuous moderate-intensity exercise potently reduces CV risk factors and oxidative stress17, 18). However, there is no study reporting whether accumulated exercise has the same effect as continuous exercise on oxidative stress.
The aim of this study was to determine if several short bouts of exercise can achieve the same effects on cardiovascular risk factors in sedentary male Japanese workers as single long bouts of exercise during a period of 20 weeks and to compare the relative effects of these exercise programs on oxidative stress.
Flowchart for participants.
This was a non-blinded randomized controlled study. Twenty-three sedentary male Japanese workers with a mean ( ± SD) age of 43.9 ± 11.6 years were recruited through the university newsletter. The inclusion criteria specified men who did not participate in any vigorous physical activity (reported exercising <20 min·d−1 on <3 d·wk−1 for the previous 6 months). We also included workers who had some cardiovascular risk factors (e.g., obesity, mild hypertension, controlled diabetes, and dyslipidemia) but not a history of cardiovascular disease or of musculoskeletal problems preventing the use of a cycle ergometer. All subjects had sedentary jobs. Medication levels were not modified during the study period. Workers were randomly assigned using random numbers generated by a personal computer to one of the following exercise programs: the Long-bout group, which performed a single period of continuous exercise for 30 min on 3 days per week, or the Short-bouts group, which performed 3 short bouts of exercise, 10 min each, on 3 days per week. A flowchart depicting the participant selection is shown in Fig. 1. All subjects provided written informed consent to participate in the present study. This study was approved by the ethics committee of the University of Occupational and Environmental Health, Japan.
Clinical assessmentAll subjects underwent complete clinical examination at baseline, after 10 weeks, and again after 20 weeks. Body weight and height were determined using a portable scale and body mass index (BMI) was calculated by dividing the weight (kg) by the square of the height (m2). Waist circumference was measured using a standard protocol19). Resting blood pressure with the subject seated was measured 3 times between 8:00 AM and 10:00 AM using an automatic sphygmomanometer (BP-203RVIII; Nihon Colin, Tokyo, Japan). The mean of the 3 blood pressure readings was used for further analysis.
Blood samples were collected after nocturnal fasting for at least 12 h. Total cholesterol (TC), high-density lipoprotein cholesterol (HDL-C), triglyceride (TG), fasting plasma insulin (FPI), and fasting plasma glucose (FPG) were measured. Low-density lipoprotein cholesterol (LDL-C) was calculated using the Friedewald formula (LDL-C=TC − HDL-C − 1/5 × TG). Insulin resistance was calculated using the homeostasis model assessment of insulin resistance (HOMA-IR) with the formula: HOMA-IR=FPI (µU·ml−1) × FPG (mg·dL−1) / 405. The plasma level of thiobarbituric acid-reactive substances (TBARS) was assayed using the fluorescence method, as previously described20, 21). The level of TBARS, which are byproducts of lipid peroxidation, is a biomarker of the systemic oxidative stress level and is correlated with cardiovascular disease and its risk factors22).
Maximum oxygen uptake (VO2max) was estimated using a 3-stage graded submaximal test with a cycle ergometer (ML-1800, Fukuda Denshi, Tokyo, Japan)23). A 6-lead electrocardiogram was recorded and blood pressure was monitored every 2 min during the test. The workload was increased by 35, 40, or 50 W every 3 min depending on the subject’s age and physical constitution. VO2max can be used as an index for cardiorespiratory endurance.
ProtocolBoth the Long-bout and Short-bouts exercise programs were 20 wk long and consisted of 30 min of cycle ergometer exercise per day on 3 days per week. An exercise intensity of 50% VO2max was established for each subject based on the result of the VO2max test. Exercise intensity could be calculated in watts, and the participants were instructed to practice exercising by themselves with the cycle ergometer at the proper intensity. Cycle ergometers were placed near their workplaces so that each participant could attain access to an ergometer within 5 min. VO2max was reassessed during the tenth week, and the exercise intensity was adjusted according to the 10-wk VO2max test for the remaining 10 wk. Subjects in the Short-bouts group were instructed to accumulate 30 min of cycle ergometer activity per day in 3 10-min sessions separated by intervals of ≥2 h on 3 d per week. Subjects in the Long-bout group were instructed to perform a single 30-min continuous bout of cycle ergometer activity 3 d per week. Both exercise programs were self-monitored, and the participants were encouraged to schedule their exercise times into their daily routines while at work. The subjects recorded the time of day for each exercise bout and agreed not to make changes to their diet.
Statistical analysisStatistical calculations were performed with personal computer statistical software (JMP 9.0; SAS Institute, Inc., Cary, USA). Differences in mean values were assessed using unpaired and paired t-tests for comparisons of 2 variables after confirmation of the normality of each data distribution using the Shapiro-Wilk W-test. Some data that were not normally distributed were subjected to logarithmic conversion prior to analysis. Changes in the cardiovascular risk factors and oxidative stress data were assessed using multivariate analysis of variance (MANOVA) with 2 factors, time (baseline, 10 weeks, and 20 weeks) and pattern of exercise (Short-bouts vs. Long-bout). The level of statistical significance was set at p<0.05.
In addition, the effect size (ES) was calculated using G*Power 3, which is a power analysis program designed as a standalone application to handle several types of statistical tests24). The indices of ES were Cohen’s d for the paired t-tests and f or f 2 for MANOVA25). According to standard practice, the thresholds for small, medium, and large effects were defined as d values below 0.20, 0.50, and 0.80; f values below 0.10, 0.25, and 0.40; and f 2 values below 0.02, 0.15, and 0.35, respectively25).
No medical complications occurred during the study. As shown in Table 1, with the exception of FPG, there were no significant differences in age, blood pressure, heart rate, body weight, BMI, waist circumference, VO2max, lipid profile, FPI, HOMA-IR, or plasma TBARS between the groups at baseline. There were also no differences between the groups with respect to the subjects’ smoking and drinking habits. Three subjects in the Short-bouts group and 2 subjects in the Long-bout group were taking antihypertensive medication, 1 in the Short-bouts group was using an oral anti-diabetes agent, and 1 in the Long-bout group was taking medication for hyperlipidemia (Table 1). An additional 2 subjects were taking medication for other diseases. Subjects did not alter their medications during the intervention. Thirteen of the subjects were researchers, and the others were clerical workers in the university; there was no significant difference in job type between the 2 groups (p=0.51). The percentages of the actual total exercise duration (of the 1,800 min prescribed) reported by subjects in the Long and Short-bouts groups over the entire 20 weeks were 68.9% (1,239 ± 670 min) and 55.5% (999 ± 528 min), respectively (p=0.35).
Group differences
In the Long-bout group, waist circumference and VO2max significantly improved after 20 wk, whereas the DBP after 10 weeks showed a significant increase compared with the baseline value (Table 2). The Short-bouts group demonstrated significant increases in VO2max after 10 weeks and in HDL-C after 20 weeks, whereas the DBP after both 10 and 20 wk and the SBP after 20 wk had significantly increased (Table 2). The VO2max after 20 wk showed a trend toward an increase in the Short-bouts group, with a medium ES (d=0.55), but this change did not reach statistical significance (p=0.08). Physical fitness levels increased with both multiple short bouts (2.4 ml·kg−1·min−1, 7.0%) and a single long bout (2.7 ml·kg−1·min−1, 7.1%) of exercise. Plasma levels of TBARS significantly decreased after 20 wk in the Long-bout group (Table 2). A trend towards decreased plasma levels of TBARS with a medium ES (d=0.58) was observed after 20 wk in the Short-bouts group but did not reach statistical significance (p=0.07).
As shown in Table 2, comparison [p (time × group)] between the long and short bouts of exercise showed no significant difference in the effects of the interventions on the overall variables. Moreover, the ES (f 2) values for VO2max, TC, and HDL-C were also below the medium level (0.15). Waist circumference, HDL-C, VO2max, and TBARS significantly improved in all subjects over the 20 wk, whereas diastolic blood pressure significantly increased [p (time) in Table 2].
This study highlights 2 major findings in sedentary male Japanese workers. First, the results of this study demonstrated no significant differences in cardiorespiratory fitness, anthropometry, or the lipid profile between accumulated short bouts of exercise and single long bouts of exercise even over a long-term intervention. Second, the subjects overall showed a significant reduction in oxidative stress during the exercise programs, and no significant difference in these effects was observed between the exercise programs. These findings suggest that accumulation of total exercise duration per week is more important than the length of each exercise session and thus provide an alternative for busy workers.
Effect on physical fitnessHigh levels of physical fitness have been shown to reduce the risks of cardiovascular disease, diabetes mellitus, and some types of cancer in male Japanese workers26,27,28). Therefore, it is important for occupational health to promote physical fitness among workers to prevent in-office deaths and decreased productivity due to these diseases29,30,31). The present study demonstrated that physical fitness levels, as indicated by VO2max, increased in response to both short bouts (2.4 ml·kg−1·min−1, 7.0%, p=0.08, d=0.55 [a medium ES]) and long bouts (2.7 ml·kg−1·min−1, 7.1%, p=0.01, d=0.90 [a large ES]) of exercise. In a long-term intervention study by Jakicic, et al., physical fitness levels in overweight women increased by 6.3% and 9.9% after 72 wk of short-bouts or long-bout exercise, respectively, with no difference between the exercise groups7). Recently, Osei-Tutu et al., reported that physical fitness levels increased by 7.2% in the Short-bouts group and by 6.7% in the Long-bout group in studies conducted over 8 weeks in sedentary men10). The results of the present study investigating the improvements in physical fitness over 20 wk in sedentary male workers are consistent with those of these previous studies.
On the other hand, a previous study reported that physical fitness in sedentary healthy men who jogged for 30 min/d on 5 days per week for 8 wk increased by 7.6% in a Short-bouts group and 13.9% in a Long-bout group, a significantly greater increase in the Long-bout group6). Murphy et al., have shown improvements in physical fitness in response to either 3 short bouts (14.2%) or 1 long bout (3.8%) of brisk walking for 10 weeks in sedentary women, but this increase was greater in the group walking for short bouts8). These differences may be due to the exercise intensities used in each study. For example, the exercise intensities (>70% maximum heart rate) in the studies cited above were higher than the intensity used in the current study (50% of maximal oxygen consumption, ≤70% maximum heart rate). Further study is needed to clarify the effects of the mode and intensity of exercise on physical fitness.
Effects on fat distribution, lipid profile, and other cardiovascular risk factorsThe Long-bout group demonstrated a significant decrease in waist circumference after 20 wk compared with the baseline value, but the decrease in waist circumference in the Short-bouts group showed a small ES (d=0.40) and did not reach statistical significance. BMI was unaltered in both groups. The decreases in waist circumference in the Long-bout group could indicate a potential alteration in the distribution of body fat away from the waist, which may lower the risk of cardiovascular disease. An interventional study by Osei-Tutu et al., also reported that only long-bout walking produced significant reductions in the percentage of body fat10). However, there are some reports that exercise patterns do not influence the magnitudes of anthropometric changes7,8,9). These inconsistencies may be attributed to population differences in parameters such as the pre-intervention waist circumference.
The Short-bouts group in the current study demonstrated a significant increase in the HDL-C level after 20 wk, but the HDL-C level in the Long-bout group showed a small ES (d=0.39) and was not significantly different. Increases in HDL-C may reduce cardiovascular risk. However, findings from other studies vary regarding the effects of brisk walking (whether accumulated through short bouts or through longer sessions) on serum lipid levels. While some studies report changes in response to both patterns of exercise9), others do not32). These inconsistencies may also be attributed to population differences in parameters such as the pre-intervention lipid profile12).
No changes in other cardiovascular risk factors (TC, TG, LDL-C, or glucose metabolism) were observed in the 2 exercise groups in this study. Eriksen and colleagues have reported that short bouts of exercise are preferable to a single continuous exercise period with regard to their effects on glucose metabolism32), but the intensity of exercise in that study (60% to 65% of maximal oxygen consumption) was higher than that used in the current study, suggesting that this difference in exercise intensity might explain the inconsistencies.
Effect on oxidative stressThe current study showed almost identical reductions in plasma levels of TBARS between the exercise groups over the 20-wk study period, based on the findings of no significant difference in the effects of the interventions when the long and short bouts of exercise were compared and on significant improvements in plasma levels of TBARS in all subjects over the 20 wk. The plasma levels of TBARS after 20 wk tended to be lower in the short-bouts group; although this trend did not reach statistical significance (p=0.07), the ES was medium (d=0.58), suggesting possible practical implications. Despite other studies that have reported the efficacy of 1 continuous exercise period33, 34), to our knowledge, no other studies have examined whether the total accumulated exercise duration could suppress oxidative stress. Oxidative stress is closely associated with the pathogenesis and the progression of cardiovascular risk factors13,14,15,16). Thus, from the perspective of occupational health for busy workers, it is highly significant that the total accumulated exercise duration may limit cardiovascular risk through the reduction of oxidative stress.
Strength and limitationsThis study has several strengths. First, this was a randomized controlled study. Second, the subjects of this study were middle-aged male Japanese workers. There have been few studies that focused on the comparison between short and long bouts of exercise using data from Japanese workers. Third, the exercise programs used in this study were tailor-made exercise programs of moderate intensity, which was measured objectively by the cycle ergometer. However, this study also has several limitations. First, this study did not have a control group despite the random assignment of the interventional groups. The aim of this study was to compare the effects of short-bout and long-bout exercise on cardiovascular risk factors, and a single continuous exercise session lasting 30 min is generally recognized as a non-pharmacologic therapy for lifestyle-related diseases. Therefore, in this study, the Long-bout group was considered the control group. Second, in the Short-bouts group, a significant increase in blood pressure in comparison with baseline was observed after 20 wk. This interventional study began in June, and the laboratory follow-ups were held in September (after 10 wk) and December (after 20 wk). Blood pressure is known to vary with the time of year, and the odds ratio for a systolic blood pressure ≥ 120 mm Hg is 1.24 for winter versus summer months35). Such seasonal changes in blood pressure may explain the unexpected increase associated with short bouts of exercise. However, the blood pressure levels in the Long-bout group were unchanged, suggesting a suppressive effect of continuous exercise on the seasonal increase in blood pressure. Third, this study is limited by the relatively small sample size. A larger sample would be necessary to establish full equivalence between the effects of 3 short bouts of exercise and 1 longer bout of exercise36, 37). Moreover, all of the ES (f 2) values in Table 2 except those for VO2max, TC, and HDL-C were either large or medium. Therefore, based on the results of the current study, exercise in short bouts cannot be deemed as effective as long-bout exercise. Finally, the rates of adherence to the prescribed exercise programs were 60% to 70%, but there was no dropout. Low exercise compliance may explain the small effects of exercise on cardiovascular risk factors, including the smaller-than-expected improvements in lipid profiles and glucose metabolism. Moreover, the adherence rate in the Short-bouts group was unexpectedly lower than that in the Long-bout group, although the difference was not significant. Because the participants in this study included researchers from the university who make frequent business trips, it may have been difficult to practically implement the short-bouts exercise program using a fixed cycle ergometer. These results also imply that occupational practitioners should match the exercise program, either short or long bouts of exercise, to the participant’s work-style.
We have demonstrated in this study that it is the performance of an exercise program itself rather than the exact nature of the program that is effective for improving physical fitness, the lipid profile, and oxidative stress and that short-bout exercise protocols are an option, especially for busy workers, for incorporating exercise into one’s lifestyle. A larger-scale randomized controlled test should be planned to determine the equivalence between the effects of 3 short bouts of exercise versus 1 longer bout of exercise.
